This is a renewal of a Harvard Medical School Training Program in Molecular Hematology. The program is designed to train graduate students, physicians and other biomedical scientists for academic careers focused on the study of the blood and its disorders. For this program a group of distinguished faculty members have come together to serve as preceptors for the students and postdoctoral fellow trainees. The program is organized around five major disciplines relevant to the broad field of Hematology-Erythroid Biology, Hemostasis/Vascular Biology, Hematopoiesis/Molecular Oncology, Immunology/Inflammation, and Genetics/ Molecular and Cellular Biology. The program selects the most promising candidates for training from a large pool of graduate students and postdoctoral fellows training at HMS and its affiliated hospitals. After nomination by a potential preceptor or program leader, trainee qualifications and research proposals are reviewed by a Steering Committee, with final appointments made by the program Co-Directors. The major training sites are the preceptor laboratories although a rich cornucopia of seminars is also available within the HMS community. Each trainee's progress is closely monitored, and reappointment is contingent'on satisfactory progress. During the past two granting periods, 73% of the program's graduates have gone on to successful academic careers. Of these, 57% currently have funded basic science laboratories. The current trainees and the program's graduates have written a total of 245 scientific papers;many in the highest quality peer-reviewed journals. The renewal application requests a modest increase in the number of funded positions for pre and postdoctoral trainees, as the number of qualified applicants far exceeds the available positions in the current grant. Diseases of the blood are among the most common disorders in man. Iron deficiency, disorders of hemoglobin production, bleeding and thrombotic disorders are good examples. In addition, some of the less frequent disorders like the leukemias and myeloproliferative disorders are models that have advanced our understanding of other forms of cancer. Finally, study of the bone marrow has become of great interest in developmental biology and is the most reliable source of adult stem cells for therapeutic studies. Since the number of trainees entering Hematology is declining grants like this are critically important for the field. (End of Abstract)